Method of producing rubber tubes



sept. 4. v19:28.4 1.682.923

C. El. MAYNARD f METHOD OF PRODUCING RUBBER TUBES Filed Apri; 16, i926 Y; ig. 4'. 779.5'.

` NVEN latented Sept. 4, 19284.

ATENT OFFICE..

v'cuantas EDGAR MAYNARD, or NoBTrfrnMrToN, MASSACHUSETTS, AssIGNoB To THE OF MASSACHUSETTS. v.

METHOD or BRODUCING RUBBER TUBES.

Application filed April 16, 19261' Serial No. 102,458.57'

This invention relates to the manufacture 'of rubber tubes, particularly such as are intended for use as inner tubes for automobile tires. The main object of thisl invention is the production of rubber tubes .upon mandrels without the necessity for -using external wrapping, clamps, or socalled cuffs, upon the outer surface of the tube. In prior practice tubes` which are vulcanized upon niandrels have either been' wrapped down against the mandrel by a spiral wrapping of fabric tape throughout their'length, or the ends of the tubes have been bound to the mandrel by some such device as metallic clamping members or by a taping of the ends only of the tube. The use of such expediente is Lavoided by my present invention. It is a v further object of my invention to provide an edective way of preventing entrance between the tube and the mandrel of'the fluid which is used for supplying vulcanizing heat to the tube. It is a further objectief the invention to accomplish the above results without the' necessity of increasing the number of manual operations necessary to perform in preparing the tube for vulcanization. It is a further object of the invention to accomplish these results without injuring the appearance of the tube. n I Referring to the drawings,

Fig. 1 is a diagrammatic front elevationl -of a mandrel illustrating the way in which it is treated prior to the rolling of the tube thereon;

Fig. 2 is a diagrammatic side elevation of the. same;

. Fig. 3 is a diagrammatic perspective view showing. the rubber sheet4 and the mandrel associated prior to the rolling of the tube -upon the mandrel;

Fig. 44 's an enlarged .detail section of a portion ofthe mandrel;

, cement, allow the cement to dry, and locate Fig. 5 is a similar view at a later stage;

Fig. 6is a similar view at a ystill later stage;

Fig. 7 is a detail view of a portion of the surface of the tube which was cured adjacent the mandrel; and

Fig. 8 is a section online 8-8 of Fig. 7.

In practicing my invention I apply either to the mandrel or to the rubber sheet which is toxbe rolled thereon a-layer of adhesive rubber, conveniently in-the form of rubber the, tube upon ythe mandrel with this adhesive area between the outer surface of the mandrel and the inner surface of the tube at a point substantially adjacentA the end of the tube. Preferably this cement is -of a low. rubber and low solvent composition so as to avoid difficulty due to the liberation of gas during the cure. Preferably, also, the cement is applied to the mandrel rather than to the rubber stock as it is much easier .to

apply and to insure drying. Preferably, also, the cement is applied in a fseries of bands as I have found that more ready and accurate application of cement can be had if y it is applied in this form. After the adhesive rubber hasbeen introduced by this or other methods between the tube and the mandrel, the mandrel 'with the tube upon it is placed in a heater surrounded by a heating fluid, such as steam or water, and subjected tothe heat -from this fluid fora length of time sufficient to vulcanize the rubber. This Huid, asis customary, is kept under pressure and the pressure serves .to force the cement into a very thin layer which tightly seals the end of the tube against entrance ofthe heating fluidv between it and the mandrel.

An apparatus for applying the cement to the mandrels is disclosed in my application Serial No. 167,946, filed February 14, 1927, and is indicated only diagrammatically in the present case. In Figs. 1 and 2 the mandrel 10 is shown as supported by tracks 11 uponpwhich are placed stops 12. As the mandrel rolls down the track it runs upon rods 13 which are coated with a liquid rubber cement.' These rods are mounted upon a frame 14 and are normally lowered, as shown in full lines in Fig. 2, into a tank 15 containing liquidA rubber cement 16. Preferably the rods are raisedout of the tank a short time before the mandrel reaches them so that the 'cement vhas a chance to drain off Ycontraction of the cement as indicated at 18 in Fig. 5.

The mandrel is now ready for the rolling operation. A strip of rubber 19 is placed upon a suitable rolling table 20. The mandrel, with-the dried cement strips 18, is now placed on one edge ot the rubber strip as indicated in Fig. 8, and a tension bar 21 is placed. upon the other edge of the strip. `The rolling operation is now started, the

rubber' stock adhering to the mandrel and to the cement strips.

After the stock has passed around the mandrel enough to give a grip, the mandrel is pulled away trom the tension bar 21`so as to give lateral stretch to the rubber stock. The rolling is then completed, the stock. bythis means being placed under a tension which causes it to contract" upon the mandrel and 4to torce itseliI down rmly upon the cement strips 18;.

Preferably 'the mandrel is kept warm-as warm as convenient to handle-before the 4cementing operation,' as the cement on a warm mandrel will dry without the necessity of any special drying step other than a slight allowance et time. ln some cases it is desirable,'in order to make a more perfect seal between the rubber and the mandrel, to havel some ofthe cement strips wider than the others. If thelsize of the rods 13 vis increased to increase the size of the cement strips, it will be found that the thickness of the nement deposit will be increased over that` of the strips deposited by the narrow rods. This` is obviously not desirable asv a `uniform thickness of vcement upon the end of the tube will give more uniform results. To accomplish the desired object without increasing the thickness of the cement, 'two rods are placed fairly close together at a point where the wide cement strip is desired. ln the drawings the two rods adjacent each end of the mandrel are shown as having this decreased spacing. As the cement settles upon the mandrel., after hailing been applied land during the drying operation, the separate strips deposited by these two end rods will merge together, as shown at the lett in Fig. 5. This same condition is preserved when the rubber sheet is rolled upon the mandrelas shown in Fig. 6.

The tube on the mandrel is now ready for vuleanization, and tor this purpose is placed in a suitable vulcanizer and subjected to an enveloping heated fluid such as steam or water under pressure. The pressure of the fluid compacts the tube against the mandrel and flattens out the cement strips still further. As the cure proceeds the cement strips will become completely merged inthe wall of the tube so that, if the Icomposition of the cement is chosen properly with relation to the composition of the tube, there will ybe little' if any contrast in appearance upon the surface of the linished tube at the points where the cement strips were located. ln Fig. 7 the appearance of the cement strips lon the finished tube has been indicated at 22,

Lasagne tion ot' thesestrips will not be as apparent as has been indicated by the drawing. A section through the wall of the inner tube is shown in Fig; 8, where it is apparent` that the cure and the pressure of the enveloping fluid hascaused the rubber to form a homogeneous mass merging into Yone piece the plies ot' the rubber sheet'l9 and the cement bands 18..

Asmentioned above, it is desirable to employ a cement having a low rubber content. 'lhe lower the rubber content oif the cement, the less solvent is needed for "its solution. lf a large amount ot' solvent is present in the cement there will be trouble during the cure with the volatilization of the solvent, with resulting blisters and other detects at the point where the cement bands are located. A reduction in the amount of solvent is therefore very desirable. I have found by experiment that a suitable cement for this purpose may be made up as follows. A batch of compounded rubber is rst formed of, the following composition:

. Partsby Weight. Off color rubber 40 Sulphur 3%, Zinc 2C Barytes i 136% Carbon black Q. t@

Fifty pounds of this compound are'then dissolved in 25 gallons naph-tha to make the cement. This particular 'compound is given for purposes 'of example only' and the in- Vention is not limited to the use of this enact formula. .instead of cementing the mandrel it is possible to apply the cement to the rubber stoort the object in either case being to intcrpose a layer of cement between the rubber. stock and the mandrel. In general, however, the application orx cement to the rubber will not be as desirable as applying it' to the mandrel-tor the reason that the use ot a heated mandrel greatly facilitates the drying operation if the cement is applied to it,

lwhich comprises applying bands of cement to a mandrel, drying the cement, rolling a sheet of rubber around the mandrel with the ends of the sheet overlying the bands, and

' vulcanizing the tube upon the mandrel with out external confining meansother than the enveloping atmosphere.

3.- A method-.ot producing a rubber Atube which comprises applying to a mandrel encircling bands of rubber cement spaced apart slightly less than the len,'gth`or1 the -tube to be made, drying the cement, rolling 'under tension around the mandrel asheet of rubber with its-ends overlying'the bands of cement, and vulcanizlng the tube onl the mandrel in an enveloping atmosphere of heated fluid, the entire outer surface of the tube being exposed directly to the action of the `fluid, whereby entrance ofthe fluid bevtween the tube and the mandrel is prevented by the cement Without the necessity of external confining means.

4. A method of producing a rubber. tube on a mandrel which comprises applying groups of vspaced bands` of rubber cement adjacent each `endof the mandrehrolling a sheet of rubber around the mandrel so that the ends of the sheet overliel the groups f ofcement bands, and vulcanizing the tube on the mandrel in an enveloping heated fluid' Without external confining means.

5.' A method of roducing a rubber tube on a mandrel Whic comprises applying to Veach end of the mandrel a group of bands of cement, each group comprising two bands closely spaced and at least one other band 1 CHARLES EDGAR MAYNARD. i 

